We've all been there, go to Best Buy, Wal-Mart, Fry's, etc... you spend hours sometimes in their stores, make your purchases, and go to exit the store. You are greeted at the exit by a big burly man in a yellow shirt, or a group of 'Receipt Checkers' who want nothing more than to, "Make sure you got everything you paid for." Of course the cashier will always say, "Please show your receipt at the door." Note* the word 'please', and note that they say 'receipt'.
This is 100% pure horseshit. We all know what they're doing is making sure you didn't steal anything, but is what they're doing legal? The short answer is no... you don't have to show your receipt, and you don't have to open your bags. Plain and simple, it's not compulsory and it violates the fourth Amendment of our Constitution. They almost always try to be polite so as to make it voluntary.
What they're doing is two things: Looking to see if you stole something, and looking for 'booster' bags or boxes. A booster bag or box is a seemingly legit looking bag or box lined with foil which circumvents those door security anti-theft devices companies put in their products. I must first recommend against employing said devices, as in most states you can be charged with 'theft-tools' which in many states is a felony. That being said, if you're a thief and you get caught, I have no advice for you. Many high target stores have rings of thieves that employ 'booster' devices to rip them off. They usually case a store and leave with nothing in their booster bags / boxes to check the security of a target. A store that can catch one, can reasonably believe that they are about to become a theft target.
If however you're an honest Joe / Jane, and you've made a purchase, the the bag and all of its contents are yours once you're handed the receipt... your personal property. You do not have to consent to a search therefore without a warrant. I am not a lawyer, but a former police officer. You will not find a legit police officer willing to search someone without probable cause because its a wide open lawsuit for unlawful detention / imprisonment. The only time I've ever seen a grey legit sign was in either a court house, federal installation, or a military post.
As I said before, to stop someone, most states require that either a felony will be committed, or that a misdemeanor 'has' been committed. So what that means is this:
Security Officer Joe observes Mike in a closed off area of the store where the value of common goods exceeds felony value and a good disappears when Mike leaves the area within a reasonable amount of time, or Security Officer Joe observes Mike placing an item in a bag, pocket, etc wherein the value of the good is less than that of a felony charge. The difference between the two, is that for the felony, Joe only has to suspect with a reasonable doubt, (Mike was the only one in the area when the felony valued good disappeared or video surveillance shows him / her pocketing the item) and for misdemeanor Joe must observe mike from the 'pocketing' or 'boosting' of the misdemeanor valued good from the point of the theft to past the last point of possible purchase (exit door).
Now, a caveat here is this "Merchant Law" which I've heard of, but no one's been able to cite (Police or DA) in any state the statute for that entitles a merchant to check your bags. That being said, I've lived in New York, California, Washington, and Florida wherein no such laws exist. I have a pretty hard time believing that any court will trump the Constitutional rights of the USA for Best Buy or CostCo. If anyone can cite one of these said merchant laws... I'm all ears.
What to do if you're stopped at a door:
1. Politely decline a search... don't be an ass.
2. If you're using their shopping cart remove your bags from said cart and invite them to inspect the empty cart.
3. If they demand a search, ask if you're being detained or arrested.
4. If they admit you're being detained or arrested, demand a police officer and note the time.
5. If the detainment time exceeds your state's statute, then profit from a small claims suit. (most states regulate this to be around $2,000.00)
Again, this is not for thieves, this is for citizens who wish not to disprove that they are in fact thieves.